Apparatus and method for high-speed SAS link protocol testing

ABSTRACT

An apparatus for changing a connection between two serial components on the same circuit board. The apparatus comprises at least one column, and each column includes first, second, third and fourth pads. The first pad communicates with a first breakout connector disposed on the circuit board. The second pad communicates with a second breakout connector disposed on the circuit board. The third pad communicates with one of the serial components. The fourth pad communicates with the other of the serial components and with the third pad during normal operation.

FIELD OF THE DISCLOSURE

This disclosure relates generally to information handling systems, andmore particularly to an apparatus and method for testing a high-speedserial attached SCSI protocol link.

BACKGROUND

As the value and use of information continues to increase, individualsand businesses seek additional ways to process and store information.One option available to users is information handling systems. Aninformation handling system generally processes, compiles, stores,and/or communicates information or data for business, personal, or otherpurposes thereby allowing users to take advantage of the value of theinformation. Because technology and information handling needs andrequirements vary between different users or applications, informationhandling systems may also vary regarding what information is handled,how the information is handled, how much information is processed,stored, or communicated, and how quickly and efficiently the informationmay be processed, stored, or communicated. The variations in informationhandling systems allow for information handling systems to be general orconfigured for a specific user or specific use such as financialtransaction processing, airline reservations, enterprise data storage,or global communications. In addition, information handling systems mayinclude a variety of hardware and software components that may beconfigured to process, store, and communicate information and mayinclude one or more computer systems, data storage systems, andnetworking systems.

Serial attached small computer system interface (SAS) is a serialpoint-to-point topology commonly used in server and storageenvironments. A problem in both environments is the testing ofhigh-speed protocol links without degrading the signal. In many serialpoint-to-point topologies, breaking out the link to a protocol analyzeris not a challenging feat. For example, a protocol analyzer can beeasily connected to a host controller or a hard drive.

In the SAS topology, point-to-point links running between chips on thesame board are common. Moreover, even the smallest stub on the line canhave dramatic effects on the signal quality and overall robustness ofthe platform. A more complex solution must be found for breaking outlinks that normally would not route to an off board connector.

BRIEF DESCRIPTION OF THE DRAWINGS

It will be appreciated that for simplicity and clarity of illustration,elements illustrated in the Figures have not necessarily been drawn toscale. For example, the dimensions of some of the elements areexaggerated relative to other elements. Embodiments incorporatingteachings of the present disclosure are shown and described with respectto the drawings presented herein, in which:

FIG. 1 is a schematic view of a circuit board including SAS expanderchips and breakout connectors;

FIG. 2 is a plan view of a portion of a circuit board similar to thatshown in FIG. 1; and

FIG. 3 is a plan view of a portion of the circuit board shown in FIG. 2and showing pair of breakout connectors.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION OF DRAWINGS

The following description in combination with the Figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings.

FIGS. 1 and 2 show a circuit board 10 for an information handlingsystem. For purposes of this disclosure, the information handling systemmay include any instrumentality or aggregate of instrumentalitiesoperable to compute, classify, process, transmit, receive, retrieve,originate, switch, store, display, manifest, detect, record, reproduce,handle, or utilize any form of information, intelligence, or data forbusiness, scientific, control, or other purposes. For example, aninformation handling system may be a personal computer, a networkstorage device, or any other suitable device and may vary in size,shape, performance, functionality, and price. The information handlingsystem may include random access memory (RAM), one or more processingresources such as a central processing unit (CPU) or hardware orsoftware control logic, ROM, and/or other types of nonvolatile memory.Additional components of the information handling system may include oneor more disk drives, one or more network ports for communicating withexternal devices as well as various input and output (I/O) devices, suchas a keyboard, a mouse, and a video display. The information handlingsystem may also include one or more buses operable to transmitcommunications between the various hardware components.

The circuit board 10 includes a plurality of SAS expander chips 12 and aplurality of breakout connectors 14, 16, 18 and 20. Transmit and receive(TX/RX) circuitry 22, 24, 26 and 28, as is well known in the art,interconnects the SAS expander chips 12 and pins near the breakoutconnectors. Further details of one example of such pins are shown inU.S. Patent Application Publication No. 2004/0196062, the disclosure ofwhich is hereby incorporated by reference.

FIG. 3 shows the breakout connectors 14 and 16 in greater detail. Fourcolumns 30, 32, 34 and 36 are disposed between the breakout connectors.The columns 30, 32, 34 and 36 correspond to TX+, TX−, RX− and RX+electrical paths, respectively. Each column includes four pads 38, 40,42 and 44. The uppermost pad 38 is in electrical communication with aTX/RX pad 46 of the breakout connector 14, while the lowermost pad 44 isin electrical communication with a TX/RX pad 48 of the breakoutconnector 16. During normal operation of the circuit board, the pads 40and 42 are in electrical communication, such as through an AC couplingcapacitor. The resulting electrical path from an SAS expander chip 12 isthus through the TX/RX lines 24, pad 40, the capacitor, pad 42, and outthrough TX/RX lines 22 to another SAS expander chip.

To insert a protocol analyzer in series such as for testing, the innerpads 40 and 42 are depopulated, i.e. the electrical connection betweenthem is broken. Instead, the two outer pairs of pads 38, 40 and 42, 44are populated, i.e. an electrical connection is established between themsuch as with capacitors. This operation establishes electricalcommunication with the pads 46 and 48, and thus the breakout connectors14 and 16 are in series with the SAS expander chips 12 such that theprotocol analyzer may be easily and usefully engaged.

Without the breakout links, it would be impossible to debug an issuebetween the two on board SAS devices. This solution does not add anycost to the board and preserves the entire signal integrity of the linkwhile providing an easy method to view the protocol transactions of thelink. Although only a few exemplary embodiments have been described indetail above, those skilled in the art will readily appreciate that manymodifications are possible in the exemplary embodiments withoutmaterially departing from the novel teachings and advantages of theembodiments of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of theembodiments of the present disclosure as defined in the followingclaims. In the claims, means-plus-function clauses are intended to coverthe structures described herein as performing the recited function andnot only structural equivalents, but also equivalent structures.

1. An apparatus for changing a connection between two serial components on the same circuit board, the apparatus comprising: at least one column, each column including first, second, third and fourth pads; the first pad communicating with a first breakout connector disposed on the circuit board; the second pad communicating with a second breakout connector disposed on the circuit board; the third pad communicating with one of the serial components; and the fourth pad communicating with the other of the serial components and with the third pad during normal operation.
 2. The apparatus of claim 1 wherein communication between the third pad and the fourth pad is broken, and the third pad communicates with the first pad, and the fourth pad communicates with the second pad.
 3. The apparatus of claim 1 wherein the column is disposed on the circuit board between the first breakout connector and the second breakout connector.
 4. The apparatus of claim 1 further comprising second, third and fourth columns disposed on the circuit board.
 5. The apparatus of claim 1 wherein the first pad communicates with a TX/RX pad of the first breakout connector, and the second pad communicates with a TX/RX pad of the second breakout connector.
 6. The apparatus of claim 1 wherein the fourth pad communicates with the third pad through a capacitor.
 7. A circuit board comprising: a first serial component and a second serial component; a first breakout connector and a second breakout connector; at least one column, each column including first, second, third and fourth pads; the first pad communicating with the first breakout connector; the second pad communicating with the second breakout connector; the third pad communicating with the first serial component; and the fourth pad communicating with the second serial component and with the third pad during normal operation.
 8. The circuit board of claim 7 wherein communication between the third pad and the fourth pad is broken, and the third pad communicates with the first pad, and the fourth pad communicates with the second pad.
 9. The circuit board of claim 7 wherein the column is disposed between the first breakout connector and the second breakout connector.
 10. The circuit board of claim 7 further comprising second, third and fourth columns.
 11. The circuit board of claim 7 wherein the first pad communicates with a TX/RX pad of the first breakout connector, and the second pad communicates with a TX/RX pad of the second breakout connector.
 12. The circuit board of claim 7 wherein the fourth pad communicates with the third pad through a capacitor.
 13. The circuit board of claim 7 wherein the serial component comprises a serial attached SCSI expander chip.
 14. A method for testing a link between two serial components on the same circuit board, the method comprising: providing at least one column, each column including first, second, third and fourth pads; providing a first breakout connector disposed on the circuit board and communicating with the first pad; providing a second breakout connector disposed on the circuit board and communicating with the second pad; connecting the third pad and one of the serial components; connecting the fourth pad with the other of the serial components and with the third pad for normal operation; breaking the connection between the third pad and the fourth pad; and establishing a connection between the third pad and the first pad, and between the fourth pad and the second pad.
 15. The method of claim 14 wherein the column is disposed on the circuit board between the first breakout connector and the second breakout connector.
 16. The method of claim 14 further comprising providing second, third and fourth columns disposed on the circuit board.
 17. The method of claim 14 wherein the first pad communicates with a TX/RX pad of the first breakout connector, and the second pad communicates with a TX/RX pad of the second breakout connector.
 18. The method of claim 14 wherein the fourth pad is connected to the third pad with a capacitor. 